There is widespread use of refrigeration units on truck-drawn trailers for cooling the storage chambers in these trailers as food or the like is transported. A common type of refrigerator presently in use is the compression refrigerator which includes an engine-driven compressor with a slow heat load device, a slow cool load device, a fast load device that causes the heating or cooling to be carried out at a faster rate, and a defrost cycle for periodically defrosting the refrigeration coils for a relatively short time duration as required.
Truck-drawn trailers equipped with refrigeration units require a high degree of reliability since a failure thereof in the event of malfunction can result in damage or loss of the cargo being transported. A combination control and signal device for this purpose must therefore be durable, capable of many turn-ons and turn-offs, and shock-resistant to the extent that the truck and trailer are moved over a relatively rough course of travel.
Some attempts have been made to provide controls and signal devices for this purpose with remote controls and signals readily accessible to the truck driver. Known prior patents relating to this application are U.S. Pat. Nos. 2,766,439 and 3,309,480. These prior art patents in general rely on moving mechanical parts and electric relays with moving contacts that have a greater tendency to wear out on a malfunction after continued use.
Accordingly, it is an object of this invention to provide an improved temperature control and malfunction signal apparatus that is particularly suited for truck-drawn refrigerated trailers.
Another object of the present invention is to provide a simple, durable and reliable electronic control circuit for automatically controlling the operation of refrigeration units and particularly trailer-mounted refrigeration units.
A further object of the present invention is to provide an electronic temperature control and signal apparatus that is readily adapted to operate with existing sensors and the load devices in truck-drawn trailer-mounted refrigeration units and like applications.
Still a further object of the present invention is to provide a compact, self-contained, control unit that is readily mounted on a truck-drawn trailer-mounted refrigeration unit and capable of withstanding the shock associated with road travel.
Yet a further object of the present invention is to provide a novel solid state circuit with no moving mechanical parts for effecting temperature control and malfunction signaling for a refrigeration unit.
Still another object of the present invention is to provide a novel temperature control for refrigeration units that avoids reverse battery polarity, excessive battery voltage, electrical noise, and inductive surges from the controlled solenoids and relays typically found in the control circuits of known refrigeration units.
Yet another object of the present invention is to provide a refrigerator electronic temperature control and signal apparatus characterized by solid state comparators responsive to a temperature sensor and a temperature selector which in turn provide output signals suitable for actuating solid state switching elements controlling the power to the various load devices in a refrigeration unit, and in addition a solid state defrost cycle control circuit which permits defrost cycle operation as well as to override the defrost sensor mechanism in the event it should fail so that periodic defrosting of the coils continues.